Ink composition and inkjet printing method

Abstract

The present invention relates to an aqueous ink composition with improved storage stability and an inkjet printing process employing such an ink composition.

Description

Technical Field

[0001] The present invention relates to ink compositions having improved storage stability and inkjet printing methods using such ink compositions.

[0002] More specifically, the present invention relates to an aqueous ink composition comprising pigments, binders, crosslinking agents and polyols, and an inkjet printing method that avoids pretreatment and posttreatment steps. Background Technology

[0003] Inkjet printing is a non-impact printing method that uses electronic signals to control and guide ink droplets or streams to deposit onto a medium. This technology has become a popular way to record images on a variety of media. Some reasons include low printer noise, variable content recording, high-speed recording capability, and multi-color recording.

[0004] As inkjet printing becomes more widespread, its applications also increase, creating a demand for new ink compositions and substrates to be printed on.

[0005] Such a substrate can be used for textiles. Textile printing can have a wide range of applications, including creative logos, banners, artwork, clothing, wall coverings, window coverings, furniture decorations, pillows, blankets, flags, tote bags, garments, etc.

[0006] In addition, there is a trend towards shifting from dye-based inks to pigment-based inks. Pigment-based inks promise compatibility with various fibers (both natural fibers, such as cellulose-based fibers like cotton, and synthetic fibers, such as polyester and polyamide). Pigment-based inks also allow printing on blended fiber fabrics.

[0007] Colored water-based inkjet inks, prepared with soluble resin binders, are used for printing on a wide variety of substrates. The pigment-based colorants used in these inks are much more resistant to fading than dye-based colorants, and are therefore suitable for applications requiring exposure to direct sunlight.

[0008] However, most fabrics are porous. When printing with pigment inks on different fabrics, the pigment penetrates deeper into the fabric, resulting in a loss of color gamut and difficulty in obtaining high-density patterns. Furthermore, obtaining colored images with the desired opacity and good wash durability can be challenging, for example, due to the use of the fabric and also due to fibrous formation (e.g., fuzzy fibers extending from the fabric surface). Another disadvantage of inkjet printing with colored inks is that inkjet-printed fabrics are particularly prone to fading due to abrasion, resulting in poor durability or fastness.

[0009] To address the aforementioned problems, existing technologies suggest applying several pretreatments and posttreatments to textile substrates. For example, US2016 / 177112, WO2006 / 00384, US2014 / 0186533, US2019 / 367760, WO2020 / 005253, and WO2022 / 173425 disclose pretreatment solutions comprising cationic surfactants, water-soluble dispersants with crosslinking properties, polyurethane resins, and crosslinking agents. For example, WO2018 / 163966A1, WO2000 / 056972A1, US2002 / 0130939, and US2003 / 160851 disclose posttreatment solutions comprising cationic polymers or copolymers, surfactants, silicone derivatives, oils, waxes, plasticizers, and fabric softeners.

[0010] From a productivity perspective, pretreatment and posttreatment are disadvantageous because they increase the number of steps and costs in print production. Furthermore, environmental pollution must be considered because wastewater treatment is essential during both pretreatment and posttreatment.

[0011] In addition to pigments, water-based ink compositions used for inkjet textile printing typically also contain polymer binders and crosslinking agents.

[0012] The color strength and fastness of colored inks on textiles are typically controlled by the amount of polymer binder added to the ink mixture. However, it is difficult to achieve good fastness of colored inks on printed or coated fabrics without adversely affecting the fabric's softness by increasing the amount of binder. When the amount of polymer binder is high enough to exhibit good durability (or fastness), the fabric hand feel becomes stiff or rough. If the amount of binder is reduced to maintain the fabric hand feel, good fastness, especially for fastness to rubbing fading, cannot be achieved.

[0013] Improvements in color strength and fastness can also be achieved by increasing the amount of crosslinking agent. The crosslinking agent can be blocked to prevent premature reaction with the binder during transport and storage. However, by increasing its amount, the system becomes unstable, the blocking agent may detach on its own, and the crosslinking agent can then begin to react with the binder, thereby increasing viscosity and shortening the ink's shelf life.

[0014] Therefore, one objective is to provide a water-based ink composition that is stable during storage, easy to apply and fix onto fabrics, and will remain on the fabric when exposed to the most common cleaning and use conditions, i.e., it has high color strength and fastness.

[0015] Another object of the present invention is to provide a printing method that uses a water-based ink composition having the above advantages and preferably does not require detailed pretreatment and / or posttreatment steps. Summary of the Invention

[0016] The problem facing the applicant is to develop a water-based ink composition that allows for overcoming the aforementioned problems and can be printed onto a substrate without the need for pretreatment and posttreatment steps.

[0017] After extensive experimentation, the applicant found a solution in an ink composition comprising pigments, binders (particularly polyurethane binders), blocked crosslinking agents (particularly blocked isocyanates), and polyols.

[0018] The applicant unexpectedly discovered that the use of specific polyols selected from ethylene glycol, 1,3-butanediol, 1,5-pentanediol, triethylene glycol, trimethylolpropane, or mixtures thereof allowed the ink composition to be stabilized even under accelerated aging, resulting in better overall printing performance.

[0019] More specifically, the applicant found that the ink composition according to the invention remains stable even after accelerated aging at 50°C for 4 weeks, and exhibits improved latency, printability, and wet rubbing fastness.

[0020] Furthermore, the applicant has discovered that the ink composition according to the invention can be used in a printing process on a substrate without the need for pretreatment and posttreatment steps.

[0021] Therefore, in one aspect, the present invention relates to a water-based ink composition comprising a pigment, a polyurethane binder, a blocked crosslinking agent, and a polyol, wherein the polyol is selected from ethylene glycol, 1,3-butanediol, 1,5-pentanediol, triethylene glycol, trimethylolpropane, and mixtures thereof.

[0022] In another aspect, the present invention relates to a printing method comprising:

[0023] • A printing step in which the ink composition of the present invention is applied to a substrate;

[0024] • A fixing / drying step in which heat is applied to cause a chemical reaction between the crosslinking agent and the polyurethane adhesive in the ink composition.

[0025] In a preferred embodiment of the printing method of the present invention, the substrate is not subjected to a pretreatment step with a pretreatment solution before the printing step, nor is it subjected to a posttreatment step with a posttreatment solution after the printing step. Detailed Implementation

[0026] While the invention may be embodied in many different forms, specific embodiments thereof will be further described herein. It should be understood that this disclosure is an example of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated.

[0027] The aqueous ink composition according to the present invention comprises a pigment dispersion, a polyurethane binder, a blocked crosslinking agent, a fluid carrier, and a polyol, wherein the polyol is selected from ethylene glycol, 1,3-butanediol, 1,5-pentanediol, triethylene glycol, trimethylolpropane, and mixtures thereof.

[0028] Ink composition

[0029] pigment

[0030] Pigments refer to colorant particles that are generally insoluble in water. Suitable pigments that can be used to form the ink compositions of the present invention may include any organic or inorganic pigments known in the art, including but not limited to black, yellow, orange, brown, red, purple, blue, green, fluorescent metallic powders and polymer-bonded pigments. Pigments may also include, but are not limited to, carbon black, azo pigments, phthalocyanine pigments, anthraquinone pigments, etc. and Perynone pigments, polycyclic pigments, naphthol pigments, anthrapyrimidone pigments, quinacridone pigments, anthrathrone pigments, flavanone pigments, indigo pigments, and dimethyl methacrylate (DMMA) pigments. Azide pigments, isoindoline and isoindoline ketone pigments, quinoline phthaloyl ketone pigments, azide pigments, nitroso pigments, nitro pigments, triphenylmethane lake pigments, Pigments include azin lake pigments, metal complex pigments, natural pigments, and inorganic pigments. The pigment particles should be small enough to allow ink to flow freely through the nozzles of the inkjet printing device.

[0031] Suitable colored pigments may include, for example:

[0032] • Yellow pigments such as CI Pigment Yellow 1, 2, 3, 4, 5, 6, 10, 12, 13, 14, 16, 17, 24, 55, 61, 65, 73, 74, 81, 83, 93, 94, 95, 97, 99, 100, 108, 109, 110, 117, 120, 123, 124, 128, 129, 133, 138, 139, 147, 150, 151, 153, 154, 155, 156, 167, 168, 172, 173, 174, 175, 176, 177, 179, 180, 181, 182, 183, 184, 185, 187, 188, 190, 191, 192, 193, 194 and their mixtures;

[0033] • Red pigments, such as CI Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 39, 40, 48, 49, 50, 51, 52, 53, 55, 60, 64, 68, 81, 83, 87, 88, 89, 90, 95, 112, 114, 119, 122, 123, 136, 144, 146, 147, 14 8, 149, 150, 151, 163, 164, 166, 168, 169, 170, 161, 172, 175, 176, 202, 204, 206, 207, 210, 211, 212, 213, 214, 216, 220, 222, 237, 238, 239, 240, 242, 243, 245, 247, 248, 251, 252, 253, 254, 255, 256, 258, 261, 264 and mixtures thereof;

[0034] • Purple pigments, such as CI pigments 1, 2, 3, 5, 13, 19, 23, 25, 27, 29, 31, 32, 37, 39, 42, 44, 50 and their mixtures;

[0035] • Blue pigments such as CI Pigment Blue 1, 2, 3, 9, 10, 14, 15, 16, 18, 19, 21, 22, 24, 25, 56, 60, 61, 62, 63, 64, 65, 66 and mixtures thereof;

[0036] • Orange pigments such as CI Pigment Orange 1, 2, 5, 6, 7, 13, 14, 15, 16, 17, 19, 22, 24, 31, 34, 36, 38, 40, 42, 43, 44, 46, 48, 49, 51, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69 and mixtures thereof;

[0037] • Green pigments such as CI pigments Green 1, 2, 4, 7, 8, 10, 34, 36, 45, 47 and their mixtures;

[0038] • Brown pigments, such as CI pigments Brown 1, 2, 3, 5, 22, 23, 25, 26, 32, 38, 41, 42 and their mixtures;

[0039] • Black pigments such as CI Pigment Black 1, 7, 20, 31, 32 and their mixtures; and

[0040] • White pigments, such as titanium dioxide.

[0041] Mixtures of different colored pigments are also included. Commercially available colored pigments may include, for example, Pigment Red 122 and Pigment Violet 19 (available from Lansco Colors, Montvale, NJ, or Clariant Colors, Charlotte, NC, or Sun Chemical, Cincinnati, Ohio), Pigment Blue 15:1 (available from Fanwood Chemical, Fanwood, NJ), Pigment Blue 15:3, Pigment 15:4, Pigment Yellow 74 and Pigment Yellow 97 (available from Clariant Colors, Charlotte, NC, or Sun Chemical, Cincinnati, Ohio), etc. Other suitable pigments may include, but are not limited to, Disperse Blue 14, Disperse Blue 19, Disperse Blue 72, Disperse Blue 334, Disperse Blue 359, Disperse Blue 360, Disperse Orange 25, Disperse Yellow 54, Disperse Yellow 64, Disperse Red 55, Disperse Red 60, Macrolex Red H, Disperse Brown 27, Solvent Blue 67, Solvent Blue 70, Solvent Red 49, Solvent Red 146, Solvent Red 160, Solvent Yellow 162, Solvent Violet 10, and Solvent Black 29.

[0042] Suitable pigments may also include carbon black, a general term for carbon particles derived from the thermal decomposition or incomplete combustion of natural gas and hydrocarbons such as coal tar-based aromatic oils, mineral oils, coal tar distillates, and acetylene. Currently, over 100 different grades of carbon black are available on the market, each with its own unique set of characteristics and properties. Any acidic, neutral, and basic carbon black can be used. This includes channel black, gas black, lampblack, thermal cracking black, acetylene black, and furnace black. More specifically, suitable carbon black includes channel black.

[0043] Commercially available examples of carbon black include, but are not limited to, those available from: Cabot (Elftex 8, Black Pearls® 490, Black Pearls® 120, Monarch® 120, Monarch® 700, Monarch® 880, Monarch® 1000, Monarch® 1100, Monarch® 1300, Monarch® 1400, Mogul® L, Regal® 99R, Regal® 250R, Regal® 300R, Regal® 330R, Regal® 400R, Regal® 500R, Regal® 660R, Cab-O-Jet® 200, Cab-O-Jet® 300 and Cab-O-Jet® 400), Degussa / OrionCarbon (NIPex® 150IQ, NIPex® 150, Printex® 55, Printex® 80. Printex® 90, Printex® A, Printex® G, Printex® U, Printex® V, Printex® 140U, Printex®140V, Purex® LS 35, Corax® HP 160, Thermal Black N 990, NIPex® 160 IQ, Nipex® 170IQ, Nipex® 180IQ, NIPex® 90, Special black 4, Special black 4A, Special black 5, Special black 6, Special black 100, Special black 250, Color black FW1, Colorblack FW2, Color black FW2V, Color black FW18, Color black FW200, Color blackS150, Color black S160 and Color black S170), Columbian / Birla Carbon (Raven® 780, Raven® 5000 Ull, Raven® 1255, Raven® 2500 U, Raven® 3600 U, Raven® 3500, Raven® 5000, Raven® 7000, Raven® 1220 and Raven® 1225), Mitsubishi Kagaku KK(MA8, MAll, MA77, MA100, MA220, MA230, MA600, MCF88, #10B, #20B, #30, #33, #40, #44, #45, #45L, #50, #55, #95, #260, #900, #970, #1000, #2200B, #2300, #2350, #2400B, #2650, #2700, #4000B and CF9), Orient Chemical Industries Ltd. (Bonjet Black CW-1, Bonjet Black CW-2, and Bonjet Black CW-3) and Sun Chemical (Graphitan® 7525). .

[0044] In some embodiments, the pigment can be self-dispersed in a selected continuous phase. A self-dispersible pigment is a pigment that does not require an additional dispersant to stabilize within the polymer composition. In one embodiment, the self-dispersible pigment is a pigment that has been functionalized with a dispersant (e.g., a molecule containing hydrophilic functional groups) (e.g., by covalently bonding the molecule to the surface of the pigment).

[0045] In other embodiments, the pigment is combined with a dispersant such as a water-soluble polymer (e.g., a vinyl polymer, a polyurethane polymer). In one embodiment, the pigment is a polymer-dispersed pigment comprising a polymer adsorbed thereto.

[0046] In one embodiment, the amount of pigment in the ink composition of the present invention (by weight) is at least 0.5% by weight, for example at least 1% by weight, at least 1.5% by weight, and at least 2% by weight. In one embodiment, the amount of colorant is at most 15% by weight, for example at most 10% by weight, at most 9% by weight, at most 8% by weight, and at most 7% by weight. This includes embodiments in which the amount of colorant in the composition is from 0.5% by weight to 15% by weight, for example from 1% by weight to 10% by weight, and from 2% by weight to 9% by weight.

[0047] The pigments used in the ink compositions of the present invention may include one or more embodiments described herein.

[0048] polyurethane adhesive

[0049] In one embodiment, the polyurethane adhesive is a polyurethane polymer having side-attached hydroxyl groups attached to a backbone of the polymer and optionally side-attached neutralized carboxyl groups.

[0050] In one embodiment, the polyurethane polymer is a polyurethane polymer having side-attached hydroxyl groups attached to the polymer backbone.

[0051] As used herein, the term "side-attached group" describes the side groups of the polymer backbone (backbone). The term "terminal group" describes the group attached to the end of the polymer backbone.

[0052] In one embodiment, the polyurethane polymer has at least 51 hydroxyl groups, such as at least 60, at least 70, and at least 80. In one embodiment, the polyurethane polymer has 1000 or fewer hydroxyl groups, such as 750 or fewer, 500 or fewer, 250 or fewer, 200 or fewer, 150 or fewer, and 100 or fewer. This includes embodiments in which the polyurethane polymer has 51 to 1000 hydroxyl groups, such as 51 to 300, 80 to 200, and 80 to 100.

[0053] In one embodiment, the polyurethane polymer has zero (0) carboxyl groups. In other embodiments, the polyurethane polymer has at least one carboxyl group, such as at least 5 and at least 10. In one embodiment, the polyurethane polymer has 100 or fewer carboxyl groups, such as 80 or fewer, 60 or fewer, and 50 or fewer. This includes embodiments in which the polyurethane polymer has 0 to 100 carboxyl groups, such as 1 to 80, 5 to 60, and 10 to 50.

[0054] Polyurethane can be produced by methods known and used in the art. Typically, polyurethane polymers can be produced by reacting isocyanate compounds with polyols, ionic polyols, or combinations thereof in the presence of a catalyst.

[0055] Examples of isocyanate compounds are well known in the art and include, for example, but not limited to, 1,6-hexamethylene diisocyanate (HDI), isophorone diisocyanate, methylene diphenyl diisocyanate (MDI), and toluene diisocyanate (TDI).

[0056] Suitable examples of polyols include diols, triols, tetraols, pentylols, and oligomers having side-linked or terminal hydroxyl groups. Examples of diols include, but are not limited to, ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentanediol, diethylene glycol, triethylene glycol, and dipropylene glycol. Examples of triols include, but are not limited to, glycerol and trimethylolpropane. Examples of tetraols include, but are not limited to, tetramethylolmethane (pentaerythritol) and diglycerol. Examples of pentylols include, but are not limited to, xylitol. Examples of oligomers having side-linked or terminal hydroxyl groups include, but are not limited to, polyether polyols (e.g., polypropylene glycol), polyester polyols, polycarbonate polyols, and polyolefin polyols (e.g., polybutadiene polyols).

[0057] In one embodiment, the ionic polyol is a diol, triol, tetraol, or pentol having one or more carboxyl groups, or an oligomer having hydroxyl and carboxyl groups. In one embodiment, the ionic polyol is a dihydroxycarboxylic acid such as 2,2-di(hydroxymethyl)acetic acid, dimethylolpropionic acid (DMPA), 2,2-bis(hydroxymethyl)butyric acid, or 2,2-di(hydroxymethyl)valerate. "Ionic polymer" means a polymer containing ionic functional groups.

[0058] In one embodiment, the side-attached groups are side groups of polymers that do not have a linear chain structure, extending from and attached to the main chain, such as branched, hyperbranched, star-shaped, and dendritic polymer groups. "Branched polymer" means a polymer having secondary polymer chains branched from the main chain. "Hyperbranched" polymer means a polymer with a highly and densely branched, irregularly branched structure, and the term also includes polymers with a regularly branched structure (which are referred to as "dendritic polymers"). "Dendrotic polymer" or "dendritic polymer" means a polymer resembling a tree-like structure having a densely branched structure typically consisting of a core portion from which branches extend and having numerous terminal groups. "Star-shaped" polymer refers to a branched polymer where a single branch has multiple outwardly radiating linear chains or arms.

[0059] Branched polyurethanes can be produced, for example, by reacting diisocyanates with excess triols, pentols, and other polyfunctional polyols (e.g., with a hydroxyl functionality greater than 2), mixtures thereof with diols, and / or with ionic polyols. Methods for producing branched polyurethanes are known in the art, such as those described in U.S. Patents 4,801,553, 4,895,894, 5,863,980, US 2010 / 0222448, U.S. Patents 4,861,826, 5,334,690, 6,583,215, 6,642,303, 6,784,243, and US 2011 / 0306724.

[0060] Hyperbranched, star-shaped, and dendritic polyurethanes with side-attached carboxyl and hydroxyl groups can be prepared, for example, by stepwise polymerization of triisocyanates with polyfunctional and ionic polyols. Methods for producing hyperbranched polyurethanes are known in the art, as described, for example, in U.S. Patents 6,927,271, 7,863,375, 8,044,140, ​​and US 2012 / 0183692.

[0061] Examples of commercially available polyurethane polymers include, but are not limited to, Impranil® (available from Covestro Deutschland AG) such as Impranil DLT-C, Neboplast® (available from Safic-Alcan Necarbo BV) such as Neboplast PEU 3500, and Daotan® (available from Allnex Netherland BV) such as Daotan TW6425 / 40WA.

[0062] In one embodiment, the water-dispersible polyurethane polymer may contain one or more side-mounted carboxyl groups and will optionally undergo a crosslinking reaction by reacting the side-mounted carboxyl groups with a crosslinking agent. To prevent premature crosslinking (and thus stabilize the ink composition during storage and before use) when mixing the components of the inkjet ink composition containing the polyurethane polymer with side-mounted carboxyl groups and the crosslinking agent, the carboxyl groups of the polyurethane polymer are neutralized.

[0063] To neutralize carboxyl groups, polyurethane polymers can react with a neutralizing agent (e.g., a base) to form a carboxylate. The neutralizing agent can be used alone or in combination of two or more. Neutralizing agents as used herein are capable of separating from carboxyl groups and, in one embodiment, can be removed from the ink composition at a desired time to allow the crosslinking reaction to proceed. Examples of suitable neutralizing agents include, but are not limited to, ammonia and tertiary amines.

[0064] In one embodiment, the neutralizing agent is ammonia, such that the neutralized carboxyl group is in the form of an ammonium carboxylate salt. The ammonia neutralizing agent can be separated from the carboxyl group and removed from the ink composition (e.g., by evaporation when the composition is exposed to atmospheric conditions with or without heat) to allow the crosslinking reaction to proceed.

[0065] In one embodiment, the neutralizing agent is a tertiary amine, such that the neutralized carboxyl group is in the form of a tertiary amine carboxylate. Any tertiary amine can be used as the neutralizing agent, as long as the tertiary amine can be separated from the carboxyl group and removed from the ink composition to allow the crosslinking reaction to proceed, for example, by evaporation from the composition when exposed to atmospheric conditions with or without heat. Non-limiting examples of tertiary amines include triethylamine (TEA), 2-dimethylaminoethanol (DMEA), triethanolamine (TEA-OH), trimethylamine, dimethylethylamine (DMEA), diethylmethylamine (DEMA), dimethylisopropylamine (DMIPA), dimethyln-propylamine (DMPA), N-methylpyrrolidine, N,N-diisopropylethanolamine, N,N-diisopropylethylamine, N,N-diethylethanolamine, N-tributylamine, N-butyl-N-ethyl-N-methylamine, N-isopentyldimethylamine, N,N-diethylmethylamine, N-pentyldimethylamine, N-methylmorpholine, N,N-dimethylcyclohexylamine, N,N-dimethylisobutylamine, N,N-dimethyl-2-(2-aminoethoxyethanol), N-methyldiethanolamine, N,N-dimethylbenzylamine, trin-butylamine, etc.

[0066] In another embodiment, the water-dispersible polyurethane polymer comprises one or more side-attached carboxyl groups, which can be neutralized by reacting with an alkali metal hydroxide, such that the neutralized carboxyl group is in the form of an alkali metal (e.g., sodium, lithium, potassium) carboxylate. Examples of alkali metal hydroxides include, but are not limited to, lithium hydroxide, potassium hydroxide, and sodium hydroxide.

[0067] In one embodiment, the glass transition temperature (Tg) of the polyurethane polymer is at least -50°C, and preferably at least 0°C. In one embodiment, the Tg of the polyurethane polymer is at most 120°C, and preferably at most 50°C. In one embodiment, the Tg of the polyurethane polymer is from -50°C to 120°C, and preferably from 0°C to 50°C.

[0068] In one embodiment, the number average molecular weight (Mn) of the polyurethane polymer is at least 1,000, and preferably at least 2,000. In one embodiment, the Mn of the polyurethane polymer is at most 1,000,000, and preferably at most 100,000. In one embodiment, the Mn of the polyurethane polymer is from 1,000 to 1,000,000, and preferably from 2,000 to 100,000.

[0069] In one embodiment, the amount (by weight) of the water-dispersible polyurethane polymer having side-linked hydroxyl groups and optionally side-linked neutralized carboxyl groups in the ink composition of the present invention is at least 1 wt%, at least 2 wt%, at least 5 wt%, at least 10 wt%, and at least 15 wt%. In one embodiment, the amount of polyurethane polymer is up to 40 wt%, for example, up to 35 wt%, up to 30 wt%, up to 25 wt%, and up to 20 wt%. This includes embodiments in which the amount of polyurethane polymer in the ink composition of the present invention is from 1 wt% to 40 wt%, for example, 2 wt% to 35 wt%, 5 wt% to 30 wt%, 10 wt% to 25 wt%, and 15 wt% to 20 wt%.

[0070] The polyurethane polymer used in the ink compositions of the present invention may include one or more embodiments described herein.

[0071] Blocked crosslinking agent

[0072] As used herein, the terms “crosslinking reagent” and “crosslinking agent” are used interchangeably.

[0073] In one embodiment, the ink composition of the present invention comprises a crosslinking agent capable of reacting with the hydroxyl groups of a polyurethane polymer.

[0074] Suitable crosslinking agents capable of undergoing reaction with the hydroxyl groups of polyurethane polymers include, but are not limited to, water-dispersible blocked isocyanate compounds.

[0075] Examples of blocked isocyanates are known in the art, and include, but are not limited to: lactam-blocked isocyanates, such as ε-caprolactam, δ-valerolactam, or γ-butyrolactam-blocked isocyanates; pyridine-blocked isocyanates, such as 2-hydroxypyridine-blocked isocyanates; oxime-blocked isocyanates, such as formaldehyde oxime, acetaldehyde oxime, acetone oxime, cyclohexanone oxime, methyl isobutyl ketone oxime, or methyl ethyl ketone oxime-blocked isocyanates; and azole-blocked isocyanates, such as pyrazole, carbazole, triazole, imidazole, thiazole, etc. Isocyanates blocked with azoles and 3,5-dimethylpyrazole; malonic acid ester blocked isocyanates, such as dimethyl malonate or diethyl malonate blocked isocyanates; phenol blocked isocyanates, such as cresol, ethylphenol, butylphenol, or nonylphenol blocked isocyanates; alcohol blocked isocyanates, such as propanol or butanol blocked isocyanates; thiol blocked isocyanates, such as butyl mercaptan or dodecyl mercaptan blocked isocyanates; uretdione blocked isocyanates; acetanilide blocked isocyanates; sebacic acid ester blocked isocyanates, such as bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacic acid ester; polymer blocked isocyanates; and mixtures thereof. Pyrazole blocked isocyanates, particularly 3,5-dimethylpyrazole blocked isocyanates, are preferably used in the ink compositions of the present invention.

[0076] When the blocking agent of the isocyanate compound (crosslinking agent) is removed (e.g., at high temperatures), a crosslinking reaction can occur. The temperature at which the reaction to dissociate the blocking agent (or specifically the deblocking reaction) becomes dominant (hereinafter referred to as the "deblocking temperature") can be adjusted based on the type of blocking agent, the type of isocyanate compound to be blocked, etc. While the specific level of this deblocking temperature is not limited in any way, it is typically between 65°C and 135°C.

[0077] Examples of commercially available blocked isocyanate compounds include, but are not limited to, Imprafix® (available from Covestro Deutschland AG) such as Imprafix 2794 and Imprafix 2794 / 1; and Tanalink® (available from Tanatex Chemicals BV) such as Tanalink PCI.

[0078] The amount of crosslinking agent in the ink composition (by weight) is at least 1.0 wt%, at least 2.0 wt%, and at least 5.0 wt%. In one embodiment, the amount of crosslinking agent (by weight) is at most 20 wt%, for example at most 15 wt%, and at most 10 wt%. This includes embodiments in which the amount of crosslinking agent in the ink composition of the present invention is from 1 wt% to 20 wt%, for example from 2 wt% to 15 wt%, and from 5 wt% to 10 wt%.

[0079] In one embodiment, the crosslinking reaction between the crosslinking agent and the hydroxyl groups of the polyurethane polymer can be promoted by heat. For example, in some embodiments, the ink composition of the present invention can be applied to a substrate and then dried, whereby the crosslinking agent and the hydroxyl groups undergo a crosslinking reaction. In one embodiment, the crosslinking reaction can be promoted by applying heat to the ink after application or during the drying process.

[0080] fluid carrier

[0081] The aqueous ink composition of the present invention comprises a fluid carrier, wherein in one embodiment, the fluid carrier comprises water and optionally one or more organic co-solvents, said one or more organic co-solvents may be water-soluble organic co-solvents, water-miscible organic co-solvents, or combinations thereof. The organic co-solvents may be added alone or in combination.

[0082] In one embodiment, the organic cosolvent is a wetting agent that can reduce the evaporation rate of the water component and prevent the ink composition from drying or skinning in the nozzle of the printhead, thereby minimizing nozzle clogging.

[0083] In another embodiment, the organic co-solvent can improve the solubility of the components in the ink composition of the present invention and promote the penetration of the printed ink composition into the substrate.

[0084] Suitable water-soluble and water-miscible organic solvents include, but are not limited to, alcohols (e.g., methanol, ethanol, propanol, isopropanol, and butanol), ketones and ketols (e.g., acetone and diacetone alcohol), and ethers (e.g., tetrahydrofuran, diacetone ... Alkanes and alkyl ethers, etc.), nitrogen-containing solvents (e.g., 2-pyrrolidone and N-methyl-2-pyrrolidone), sulfur-containing solvents (e.g., 2,2'-thiodiethanol, dimethyl sulfoxide, tetramethylene sulfone and sulfolane), and sugars and their derivatives (e.g., glucose, ethylene oxide adducts of glycerol, and ethylene oxide adducts of diglycerol, etc.).

[0085] In one embodiment, the amount (by weight) of the organic co-solvent in the ink composition of the present invention is at least 1% by weight, for example at least 2% by weight, and at least 5% by weight. In one embodiment, the amount (by weight) of the organic co-solvent is at most 15% by weight, for example at most 14% by weight, at most 14% by weight, and at most 10% by weight. This includes embodiments in which the amount of the organic co-solvent in the composition is from 1% by weight to 15% by weight, for example from 5% by weight to 10% by weight.

[0086] The organic cosolvent used in the ink compositions of the present invention may include one or more embodiments described herein.

[0087] In one embodiment, the amount of water (by weight) in the ink composition of the present invention is at least 5 wt%, at least 8 wt%, at least 10 wt%, at least 15 wt%, at least 20 wt%, and at least 25 wt%. In one embodiment, the amount of water (by weight) is at most 95 wt%, at most 85 wt%, at most 80 wt%, at most 75 wt%, at most 70 wt%, at most 65 wt%, and at most 60 wt%. This includes embodiments in which the amount of water in the composition is from 5 wt% to 95 wt%, for example from 10 wt% to 80 wt% and from 20 wt% to 70 wt%. The range of water in the composition is typically from 15 wt% to 75 wt%, and more typically from 25 wt% to 60 wt%.

[0088] polyols

[0089] The ink composition according to the present invention comprises a polyol selected from the following: ethylene glycol, 1,3-butanediol, 1,5-pentanediol, triethylene glycol, trimethylolpropane, and mixtures thereof.

[0090] Preferably, the ink composition according to the invention does not contain any polyols other than ethylene glycol, 1,3-butanediol, 1,5-pentanediol, triethylene glycol and trimethylolpropane.

[0091] The polyols used in the ink compositions of the present invention may include one or more embodiments described herein.

[0092] In one embodiment, the amount of polyol in the ink composition of the present invention (by weight) is at least 1 wt%, at least 2 wt%, at least 3 wt%, and at least 5 wt%. In one embodiment, the amount of polyol (by weight) is at most 30 wt%, at most 25 wt%, at most 20 wt%, and at most 15 wt%. This includes embodiments in which the amount of polyol in the ink composition of the present invention is from 1 wt% to 30 wt%, for example, from 2 wt% to 25 wt% and from 3 wt% to 20 wt%. The range of polyol in the composition is generally from 5 wt% to 15 wt%. Most preferably, the amount of polyol in the ink composition of the present invention (by weight) is 6 wt%, 8 wt%, 10 wt%, 12 wt%, 14 wt%, or any value between these values.

[0093] additive

[0094] In one embodiment, the ink composition of the present invention may optionally contain one or more additives compatible with the other components of the composition. Additives may be included in the composition to impart any number of desired properties, including but not limited to stability, smudge resistance, viscosity, surface tension, coating penetration, optical density, color depth, adhesion, gloss pen resistance, and anti-skinning properties. Suitable additives for such applications and the amounts of such additives used are known and are conventionally used in the art.

[0095] Examples of additives include, but are not limited to, defoamers, preservatives, surfactants, pH adjusters, viscosity modifiers, wetting agents, penetrants, and additive polymers.

[0096] In one embodiment, the ink composition of the present invention may contain a defoamer to inhibit foam formation. Examples of suitable defoamers include, but are not limited to, silicone-based or non-silicone-based defoamers. Commercially available defoamers include, but are not limited to, Dow Corning® 71 and Dow Corning® 74 (from Dow Corning); TegoAirex® 901W, 902W, and 904W from Evonik Industries; and Tergitol® L-61, L-62, L-64, and L-101 (from Dow Chemical). The typical amount (by weight) of the defoamer contained in the composition is from 0.1% to 3% by weight.

[0097] In one embodiment, the ink composition of the present invention may contain a preservative, such as a biocide and a fungicide, to inhibit the growth of microorganisms. Examples of suitable preservatives include, but are not limited to, sodium benzoate, sodium pentachlorophenate, sodium 2-pyridinium-1-oxide, sodium sorbate, sodium dehydroacetate, benzisothiazolinone, 1,2-dibenzothiazolin-3-one, and 1-(3-chloroallyl)-3,5,7-triaza-1-azoline. Adamantane chloride (CTAC), methylisothiazolinone, and chloromethylisothiazolinone, etc. Commercially available biocides include UCARCIDE® 250 (available from Union Carbide Company), Proxel® CRL, Proxel® BDN, Proxel® GXL, Proxel® XL-2, Proxel® TN (available from Arch Chemicals, Smyrna, Ga.), Dowicil® (Dow Chemical, Midland, Mich.), Nuosept® (Huls America, Inc., Piscataway, NJ), Omidines® (Olin Corp., Cheshire, Conn.), Nopcocides® (Henkel Corp., Ambler, Pa.), Troysan® (CO (Troy Chemical Corp., Newark, NJ), and XBINX® (PMC Specialties Group, Inc., Cincinnati, Ohio). Preservatives can be used alone or in combination. Typical amounts of preservatives included in compositions range from 0.1% to 1.5% by weight.

[0098] In one embodiment, a surfactant may be included to reduce the surface tension of the ink composition of the present invention. The surfactant may be anionic, nonionic, or cationic. Suitable surfactants may include, but are not limited to, those listed below and in U.S. Patents 5,116,409, 5,861,447, and 6,849,111. Exemplary surfactants are commercially available under various trade names, such as the PLURONIC® series (BASF Corporation, Parsippany, NJ), TETRONIC® series (BASF Corporation, Parsippany, NJ), ARQUAD® series (Akzo Chemical Inc., Chicago, III.), TRITON® series (Union Carbide Corp., Danbury, Conn.), SURFONIC® series (Texaco Chemical Company, Houston, Tex.), ETHOQUAD® series (Akzo Chemical Inc., Chicago, III.), ARMEEN® series (Akzo Chemical Inc., Chicago, III.), ICONOL® series (BASF Corporation, Parsippany, NJ), SURFYNOL® series (Air Products and Chemicals, Inc. Allentown, Pa.), and ETHOMEEN® series (Akzo Chemical Inc., Chicago, III.). Surfactants can be used alone or in combination. The typical amount (by weight) of surfactant contained in the composition is from 0.1% to 10% by weight.

[0099] In one embodiment, a pH adjuster may be included to adjust or buffer the ink composition of the present invention to a desired pH. Suitable pH adjusters include, but are not limited to, basic hydroxides, basic carbonates and bicarbonates, triethylamine, dimethylethanolamine, triethanolamine, inorganic acids, hydrochloric acid, and sulfuric acid. The pH adjuster may be used alone or in combination. The typical amount (by weight) of the pH adjuster in the composition is 0.1% to 2% by weight. In one embodiment, the ink composition of the present invention has a pH of 7 to 10 at 25°C. More preferably, the pH is between 7 and 9. Most preferably, the pH is equal to 7.0, 7.2, 7.4, 7.6, 7.8, 8.0, 8.2, 8.4, 8.6, 8.8, or 9.0, or any value between them.

[0100] In one embodiment, the ink composition of the present invention may contain one or more viscosity modifiers. Examples of suitable viscosity modifiers include, but are not limited to, resin compounds, alginate compounds, polyvinyl alcohol, hydroxypropyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, salts of polyacrylic acid, polyvinylpyrrolidone, gum arabic and starch, hydrophobic ethoxylated carbamate (HEUR), hydrophobically modified alkali-swellable emulsion (HASE), alkali-swellable emulsion (ASE), etc. Viscosity modifiers may be used alone or in combination. The typical amount (by weight) of viscosity modifier in the composition is 0.5% to 10% by weight. In one embodiment, the ink composition of the present invention has a viscosity of 1 mPa·s to 15 mPa·s at 25°C, as measured by a Brookfield viscometer. More preferably, the viscosity is between 2 mPa·s and 14 mPa·s. Most preferably, the viscosity is 2 mPa·s, 4 mPa·s, 6 mPa·s, 8 mPa·s, 10 mPa·s, 12 mPa·s, 14 mPa·s, or any value between them.

[0101] In some embodiments, the ink composition of the present invention may optionally contain one or more conductive agents. In some embodiments, the conductive agent may be a salt (e.g., an organic salt or an inorganic salt). For example, the salt may be a quaternary salt. Salts (e.g., tetraalkyl) Salt or tetraaryl Salts), quaternary ammonium salts (e.g., tetraalkylammonium salts or tetraarylammonium salts), imidazoles Salts or alkali metal salts (e.g., Li, Na, K, or Cs salts).

[0102] Generally, the ink compositions of the present invention can have any suitable conductivity. In some embodiments, the conductivity range of the ink compositions can be from at least about 0 µS / cm (e.g., at least about 10 µS / cm, at least about 50 µS / cm, at least about 100 µS / cm, at least about 200 µS / cm, at least about 300 µS / cm, at least about 400 µS / cm, at least about 500 µS / cm, or at least about 1000 µS / cm) to at most about 8000 µS / cm (e.g., at most about 7000 µS / cm, at most about 6000 µS / cm, at most about 5000 µS / cm, at most about 4000 µS / cm, at most about 3000 µS / cm, at most about 2000 µS / cm, or at most about 1000 µS / cm). For example, when an ink composition is designed for continuous inkjet printing processes, the ink composition can have a suitable conductivity (e.g., 100 µS / cm to 8000 µS / cm) to enable the ink composition to be printed in that process. As another example, when an ink composition is designed for thermal inkjet printing processes, the conductivity of the ink composition can be zero, because conductivity is not required in that printing process.

[0103] In one embodiment, in addition to the organic co-solvent that can act as a fluid carrier component of the wetting agent, the ink composition of the present invention may also contain one or more wetting agents to reduce the evaporation rate of the water component and prevent the ink composition from drying out in the nozzle of the printhead (which may occur during the latency period), thereby minimizing nozzle clogging. The wetting agent may be selected from materials with high hygroscopicity and water solubility. Examples of suitable wetting agents include, but are not limited to, lactams (e.g., 2-pyrrolidone, urea compounds such as urea, 1,3-dimethylimidazolinone), sugars (e.g., sorbitol), 1,4-cyclohexanediol, 1-methyl-2-piperidinone, N-ethylacetamide, 3-amino-1,2-propanediol, ethylene carbonate; butyrolactone and Liponic EG-1, etc. There are no particular limitations on the amount of wetting agent used. The typical amount of wetting agent in the composition (by weight) is from 0.5% to 30% by weight.

[0104] In one embodiment, a penetrant may be included to reduce bleeding of the ink composition of the present invention when applied to a printing substrate such as paper. Examples of suitable penetrants include, but are not limited to, alkyl alcohols (e.g., ethanol) having 1 to 4 carbon atoms, formamide, acetamide, dimethyl sulfoxide, sorbitol, and sulfolane. Penetrants may be used alone or in combination. A typical amount of penetrant in the composition is from 1% to 20% by weight.

[0105] In one embodiment, the ink composition of the present invention may include additional polymers (in addition to polyurethane polymers) to enhance the water fastness, rubbing fastness, and light fastness of the ink image applied to and dried on a printing substrate. Examples of such polymers include, but are not limited to, polyvinyl alcohol, polyester, polyester melamine, styrene / acrylic acid copolymer, styrene / maleic acid copolymer, styrene / maleic acid / alkyl acrylate copolymer, styrene / methacrylic acid copolymer, styrene / methacrylic acid / alkyl acrylate copolymer, styrene / maleic acid half-ester copolymer, vinylnaphthalene / acrylic acid copolymer, vinylnaphthalene / maleic acid copolymer, and salts thereof. Such additional polymers may be used alone or in combination. A typical amount (by weight) of such additional polymers that may be included in the composition is from 0.1% to 20% by weight.

[0106] Other additives that may be included in the ink compositions of the present invention include, but are not limited to, antioxidants, ultraviolet absorbers, chelating agents, conductivity modifiers, oxygen absorbers, anticoagulants, anti-curling agents, and fragrances. The amounts of such additives used in water-based ink compositions are known and are conventionally used in the art.

[0107] Printing processes and products

[0108] Generally, the ink composition of the present invention can be used in any suitable printing process, including continuous inkjet (CIJ) printing and on-demand inkjet printing (e.g., thermal inkjet (TIJ) printing or piezoelectric printing). In some embodiments, the ink composition can be used in a printing process that includes jetting the ink composition from the printhead in an inkjet printer (continuously or on demand) onto a substrate to form an image.

[0109] Examples of suitable substrates include, but are not limited to, plain paper, laminated paper, coated paper, transparent materials, and textile materials. The ink compositions of the present invention are particularly suitable for textile substrates.

[0110] In some implementations, in continuous inkjet printing processes, a continuous flow of conductive ink droplets can be ejected from one or more nozzles of the printhead of an inkjet printer. As the substrate moves relative to the nozzles, the droplets are electrostatically deflected to address several vertical pixels. CIJ inks typically have suitable conductivity and allow for droplet deflection. The process of continuously ejecting ink droplets and directing unwanted droplets to the reservoir allows CIJ systems to utilize rapidly evaporating solvents (e.g., solvents with a relative evaporation rate (RER) greater than 1 relative to n-butyl acetate, as determined by ASTM method D3359) without concerns about decapping (i.e., the ability to maintain a fluid state in the printhead nozzle opening when exposed to air) and nozzle clogging, since the nozzles are virtually never idle during operation.

[0111] In some implementations, in continuous inkjet printing processes, the continuous stream of ink ejected from the printhead is deflected by at least one electrode subjected to an electrostatic or sinusoidal high voltage. Most of the ink stream is not printed but is directed to an ink recovery tank. During printing, segments of the ink stream are asynchronously sampled, deflected differently according to their length (length provides a method for varying the embedded charge distribution per unit length), and directed to the substrate. These segments (which can transform into spherical droplets under surface tension) separate from the jet stream before their deflection, causing their trajectories to differ from the ink stream.

[0112] In some implementations, ink can be ejected from a thermal inkjet cartridge or a piezoelectric on-demand inkjet printhead in an ink-on-demand printing process. To print, ink is loaded into a reservoir, where it is pumped or supplied by gravity to the ejection chamber of the cartridge or printhead. In the case of a thermal inkjet cartridge, liquid ink is ejected from the printhead by rapid heating, which causes a rapid phase change from liquid to gas, resulting in rapid volume expansion and subsequently causing droplets to be ejected from the orifice. In the case of a piezoelectric-based device, liquid ink is ejected from the printhead by activation of a piezoelectric transformer (PZT), which causes a pressure wave to be applied to the ink, allowing droplets to be ejected from the orifice. Both devices are referred to as on-demand inkjet because droplets are ejected only when the heater or PZT material is activated. Each cartridge or printhead includes an array of several orifices across its width. The printing press systematically activates each aperture in such an array, causing an image to be formed dropwise on a substrate positioned at a distance from the array of apertures. The printing press is designed such that the array of apertures and the substrate move relative to each other to form the image.

[0113] According to one embodiment, the present invention relates to a printing method comprising:

[0114] • The printing step of applying the ink composition of the present invention to the substrate,

[0115] • A fixing / drying step that involves applying heat to cause a chemical reaction between the crosslinking agent and the polyurethane adhesive in the ink composition.

[0116] In a preferred embodiment of the printing method according to the invention, the substrate is not subjected to a pretreatment step with a pretreatment solution prior to the printing step.

[0117] In a preferred embodiment of the printing method according to the invention, the substrate is not subjected to a post-treatment step using a post-treatment solution after the printing step.

[0118] In one embodiment, the substrate is a textile material, such as animal hair, cotton, silk, polypropylene, polyethylene, polyamides such as aliphatic polyamides (i.e., nylon-6, nylon-6,6) and aromatic polyamides (i.e., Kevlar®, Nomex®), viscose fiber, cellulose, or polyester.

[0119] The following examples illustrate some known embodiments of the present invention. However, it should be understood that the following are merely examples or descriptions of the application of the principles of the invention. Many modified and alternative compositions, methods, and systems can be devised by those skilled in the art without departing from the spirit and scope of the invention. The appended claims are intended to cover such modifications and arrangements. Therefore, while the invention has been specifically described above, the following examples, in conjunction with embodiments currently considered acceptable, provide further detail.

[0120] Experimental Section

[0121] Exemplary aqueous inkjet ink compositions are prepared, comprising pigment dispersions, surfactants, biocides, wetting agents, and various combinations of binders, crosslinking agents, and polyols, as described in Tables 1 to 6 below.

[0122] More specifically, the composition comprises the following commercially available ingredients.

[0123]

[0124]

[0125]

[0126]

[0127]

[0128]

[0129]

[0130] The performance of all ink compositions 1 to 66 was evaluated according to the following method.

[0131] Using a Brookfield DV2-T viscometer, at approximately 264 seconds -1 The viscosity of the ink composition was measured at 25°C before and after aging at 50°C for 4 weeks at a shear rate of 0.5%. The aging stability was evaluated based on the following scores based on the percentage increase in viscosity.

[0132] Very poor = greater than 60%

[0133] Difference = 30% to 60%

[0134] Acceptable = 15% to 30%

[0135] Good = 10% to 15%

[0136] Very good = less than 10%

[0137] The weight of the paper was 103 g / m³, achieved by four print runs at 30 kHz in grayscale mode using an MS JP7 printing press with a Kyocera KJ4B head filled with an ink-filled composition. 2 Printability was assessed using 50 meters of 100% cotton poplin fabric (160 cm wide). Printability was evaluated based on the following score, determined by the percentage of missing or misaligned nozzles:

[0138] Difference = greater than 2%

[0139] Acceptable = 0.5% to 2%

[0140] Good = less than 0.5%

[0141] According to the standard method UNI EN ISO 105 X12:2016, under the following conditions, the weight of 103 g / m 2 The wet rubbing fastness test of 100% cotton poplin fabric:

[0142]

[0143] The results are evaluated based on the following scores, compared with the gray levels specified in standard UNI EN 20105-A03:1996:

[0144] Difference = less than 2.5

[0145] Acceptable = 2.5 to 3.5

[0146] Good = 3.5 to 4

[0147] Very good = from 4 to 5

[0148] The delay was assessed using the same MS JP7 printing press with a Kyocera KJ4B head, based on the following score, which was determined by the percentage of nozzles that were lost or deviated 45 minutes after leaving the printing carriage from the capping station.

[0149] Difference = greater than 2%

[0150] Acceptable = 0.5% to 2%

[0151] Good = less than 0.5%

[0152] The printing process does not include any pretreatment or posttreatment of the textile substrate, but only includes the steps of printing the ink composition onto the textile substrate and fixing / drying the ink on the textile substrate at 160°C for 3 minutes.

[0153] The results are summarized in Tables 7 to 12 below.

[0154] Table 7

[0155]

[0156] Table 8

[0157]

[0158] Table 9

[0159]

[0160] Table 10

[0161]

[0162] Table 11

[0163]

[0164] Table 12

[0165]

[0166] The results summarized in Tables 7 to 12 confirm that only compositions containing the selected polyols, namely ethylene glycol (compositions 1, 12, 23, 34, 45 and 56), 1,3-butanediol (compositions 4, 15, 26, 37, 48 and 59), 1,5-pentanediol (compositions 6, 17, 28, 39, 50 and 61), triethylene glycol (compositions 9, 20, 31, 42, 53 and 64), and trimethylolpropane (compositions 11, 22, 33, 44, 55 and 66), received at least acceptable evaluations in all assessed performance aspects.

[0167] The best results were obtained with 1,3-butanediol (compositions 4, 15, 26, 37, 48 and 59) and 1,5-pentanediol (compositions 6, 17, 28, 39, 50 and 61).

[0168] It should be understood that, in view of the above description of embodiments of the present invention, various modifications can be made by those skilled in the art. These modifications are intended to be covered by the appended claims.

Claims

1. A water-based ink composition comprising a pigment, a polyurethane binder, a blocked crosslinking agent, and a polyol, wherein the polyol is selected from ethylene glycol, 1,3-butanediol, 1,5-pentanediol, triethylene glycol, trimethylolpropane, and mixtures thereof.

2. The water-based ink composition according to claim 1, wherein the polyurethane binder is a polyurethane polymer, the polyurethane polymer comprising side-attached hydroxyl groups attached to the backbone of the polymer.

3. The water-based ink composition of claim 2, wherein the polyurethane polymer further comprises neutralized carboxyl groups attached to the backbone of the polymer.

4. The water-based ink composition according to claim 1, wherein the ink composition comprises the polyurethane binder in an amount ranging from 1% to 40% by weight, preferably from 2% to 35% by weight, more preferably from 5% to 30% by weight, and even more preferably from 10% to 25% by weight.

5. The water-based ink composition according to claim 1, wherein the blocked crosslinking agent is capable of reacting with the hydroxyl groups of the polyurethane adhesive.

6. The water-based ink composition according to claim 1, wherein the blocked crosslinking agent is a water-dispersible blocked isocyanate compound.

7. The aqueous ink composition according to claim 1, wherein the blocked crosslinking agent is selected from lactam-blocked isocyanates, pyridine-blocked isocyanates, oxime-blocked isocyanates, azole-blocked isocyanates, malonic acid ester-blocked isocyanates, phenol-blocked isocyanates, alcohol-blocked isocyanates, thiol-blocked isocyanates, diurea-ketone-blocked isocyanates, acetanilide-blocked isocyanates, sebacic acid ester-blocked isocyanates, polymer-blocked isocyanates, and mixtures thereof.

8. The water-based ink composition according to claim 1, wherein the ink composition contains the blocked crosslinking agent in an amount ranging from 1% to 20% by weight, preferably from 2% to 15% by weight, and more preferably from 5% to 10% by weight.

9. The aqueous ink composition according to claim 1, wherein the polyol is selected from 1,3-butanediol and 1,5-pentanediol.

10. The water-based ink composition according to claim 1, wherein the ink composition comprises the polyol in an amount ranging from 1% to 30% by weight, preferably from 2% to 25% by weight, more preferably from 3% to 20% by weight, and even more preferably from 5% to 15% by weight.

11. The water-based ink composition according to claim 1, wherein the ink composition comprises the pigment in an amount ranging from 0.5% to 15% by weight, preferably from 1% to 10% by weight, and more preferably from 2% to 9% by weight.

12. The water-based ink composition according to claim 1, wherein the composition does not contain any polyols other than ethylene glycol, 1,3-butanediol, 1,5-pentanediol, triethylene glycol and trimethylolpropane.

13. A printing method, comprising: • A printing step in which the aqueous ink composition according to claims 1 to 12 is applied to a substrate; • A fixing / drying step by applying heat to cause a chemical reaction between the crosslinking agent and the polyurethane adhesive in the water-based ink composition.

14. The printing method of claim 13, wherein the substrate is not subjected to a pretreatment step with a pretreatment solution prior to the printing step.

15. The printing method of claim 13, wherein the substrate is not subjected to a post-treatment step with a post-treatment solution after the printing step.

16. The printing method according to any one of claims 13 to 15, wherein the substrate is a textile substrate.

17. The printing method according to claim 16, wherein the textile substrate is selected from animal hair, cotton, silk, polypropylene, polyethylene, aliphatic polyamide and aromatic polyamide, viscose fiber, cellulose and polyester.

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